I'd get this checked out especially since it is difficult for you to get a visual of it based on location. Abscesses happen. Is it painful? People do have an indentation in that area, or I should say 'some' people do. It's normal but the pus is not normal. This is in your crack, not a little further up. In looking up pilonidal abscess, it looks to be about that area. Can you go to a doctor to have it looked at?
Hello~I would certainly get it checked by your GP,it may be nothing, but for issues like this, it is always best to make sure, you may need some anti-biotic cream or pills.